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The Amana Radarange March 1955
Popular Electronics Article
March 1955 Popular Electronics
of Contents]People old and young enjoy waxing nostalgic about and learning some of the history of early electronics.
Popular Electronics was published from October 1954 through April 1985. All copyrights (if any) are hereby acknowledged.
legend goes, the use of microwaves for preparing food was pursued after
a serendipitous discovery by Raytheon engineer
Percy Spencer whereby he noticed the chocolate bar in his pocket
had melted while he was working near a radar transmitter magnetron.
Being a newly discovered phenomenon in 1945, Mr. Spencer was probably
not aware that his own body parts were being likewise cooked, but he
did recognize the commercial potential of an oven that used microwaves
to cook food. It only took Raytheon (Amana) to have the first Radarange
available for sale to professional kitchens. This article was printed
a full decade after the discovery and even then the size and power consumption
was too great for grandma's countertop. Of course grandma would never
even have considered using such a newfangled device. In fact, many people
equated the microwave's cooking action with using a nuclear reaction
to do the job, hence the term "nuking" food in the microwave. Keep in
mind that it was the era of the first atomic bomb explosions where gruesome
films were shown burning the flesh off of test animals on ships at the
Bikini Atoll. The crucial
difference between microwave radiation and nuclear radiation is that
microwaves are non-ionizing, meaning that they do not contain enough
or the right wavelength energy to knock electrons out of their orbits
(yeah, an outmoded term but it sounds cooler than probability density),
whereas decaying nuclear products do. I remember my mother's first microwave
oven (c.1975) was huge and weighted probably 30 pounds; it occupied
the full depth of a standard countertop (25"). For many years there
was a concern about microwave radiation leaks around the door gaskets
and even the chassis, but that issue has been resolved in modern appliances.
In fact, with microwave ovens operating in the same 2.4 GHz frequency
band as Bluetooth and WiFi, there was also a big discussion in the mid-1990s
about whether microwave ovens would interfere with and even prevent
those technologies from being usable. Just as Y2K (remember that?) turned
out to be a non-event, so did microwave oven interference. BTW, I took
a picture of one of the original
Radaranges on display in the
Museum at the 2009 MTT-S shown in Boston.
Only the food gets hot in the new "Radarange". Cooking utensils
and interior of oven remain cool since these materials do not
absorb the microwaves that cook the food.
Shown at left-top, floor model 1161 has completed two years
of field tests to prove its worth. This unit uses two magnetrons
to generate the microwave cooking energy.
of new unit has been simplified. Parts are readily accessible.
Note air-cooling unit at left.
Model 1170, above, is smaller of two models of "Radaranqe" now
Food can be cooked in a fraction of the time it usually requires, by
the new "Radarange" which utilizes microwave energy to heat nothing
but the food itself. Made by the Raytheon Manufacturing Company of Waltham,
Mass., the new oven can prepare an 18-pound roast of beef in 40 minutes.
At a recent demonstration, a chicken was roasted in 9 minutes; an apple
pie baked in 6 minutes; and steaks done in 1 minute. The walls of the
oven, as well as the utensils holding the food, remained cold and could
be touched with bare hands.
Designed for primary cooking, defrosting,
and reheating, the "Radarange" heats food by microwave energy generated
at 2450 megacycles, produced by QK-390 continuous wave, air-cooled magnetrons.
In model 1161, two magnetrons produce a maximum of 1600 watts; in smaller
model 1170, one magnetron produces a maximum of 800 watts. In both cases
the microwave energy is directly coupled to the oven cavity, where it
is confined by the metal walls and a door designed with appropriate
chokes. Thus, instead of the food being cooked by the conventional method
of applying heat to its surface and then waiting for the heat to be
conducted through the food, the food in the "Radarange" oven is penetrated
by the microwaves to a depth of about 2 1/2 inches. As it penetrates,
the microwave energy sets up molecular friction deep within the food
which in turn creates the heat that cooks it. This process is the key
to the tremendous reduction in time needed for cooking the food.
No physical change takes place in the food, except the normal changes
caused by the heat. And the only heat present is within the food itself.
Since the stainless steel of the oven, and the material of which cooking
utensils and plates are made resist microwave penetration, they do not
The "Radarange" oven's tremendous speed helps reduce
food wastage. For example, in estimating a restaurant's daily needs
for roasts, only enough meat for the smallest expected amount of business
is cooked by conventional methods. Should extra business develop later
in the day, extra roasts may be prepared in the "Radarange" oven in
ample time to meet the orders. In most establishments, this procedure
may be used repeatedly, keeping just "one roast ahead" of business.
Speed of "Radaranqe" is shown by cooking times
required for various dishes.
Except for the magnetrons,
all the electrical equipment in the "Radarange" runs at power frequencies
and consists of power supply and control equipment. The only tubes besides
the magnetrons are the rectifier tubes in the power supply, which furnishes
320 ma at 5000 volts to each magnetron.
Magnetrons are essentially
constant voltage devices like gas voltage regulator tubes and will draw
widely fluctuating amounts of current with very small changes in voltage.
Therefore, some means of current control is required. This control is
accomplished very simply with a saturable reactor circuit in series
with the primary of the high-voltage transformer. Using this reactor,
the magnetron circuit, and thus the cooking speed, is held virtually
constant for changes in line voltage of plus 10 or minus 5 percent from
the design voltage. The reactor is also used to provide lower oven heats
by reducing the magnetron current. This method is a particularly convenient
way to control heats, as all switching can be done in the low current
control circuit rather than in the power circuit.
Power is provided
for exhausting steam from the oven and cooling magnetrons and other
components. Considerable care has been taken to insure long life by
running the electrical components cool. The air in commercial kitchens
is usually hot, grease laden, and frequently full of lint. The electronic
components in the range operate at relatively high power and must be
kept cool if long and trouble-free operation is to be achieved. Cooling
air, therefore, is drawn in at the front, where the air is most apt
to be cool and free of grease when the range is placed in a row of other
cooking equipment. The air is then filtered and forced over the electrical
components and out through openings in the back of the cabinet.
The microwave ovens are designed to operate on 208 to 230 volts,
single phase, 60 cycles. The neutral wire carries no current and can
be used for grounding. The conversion from 208 to 230 volts is made
by changing a transformer tap within the range. The large model consumes
about 1.02 kw on standby and about 5.3 kw on high heat. The power demand
for the small model is half of that of the large range.
efficiency of the magnetron itself is about 50 percent; that is, about
half of the power supplied to the magnetron is fed into the oven as
microwave power. Over 90 percent of this power is converted to heat
in the food. The remaining 10 percent is dissipated in random heating.